johnk@opel.COM (John Kennedy) (03/02/91)
I've come across an interesting phenomenon in AT&T SVR3.2.2 and Interactive 2.2. When switching virtual screens (alt-SysRq F1, etc), I've observed that either interrupts are shut off for very long periods of time, or a DMA channel is tied up for excessively long. The net result is a loss of incoming serial data even at speeds down to 2400 baud. I am already using 16550's, so I know that over 15 characters are lost. A rough estimate of 4 ms/char x 15 tells me that interrupts are off for at least 60 ms. Test: Provide a stream of incoming data, preferably one which generates a recognizable pattern on a screen, or one that feeds a program that can compare differences in incoming patterns. Switch virtual consoles and observe the character losses. -or- Watch your modem lights on a steady UUCP transfer. Watch the lights when you change virtual consoles. John -- John Kennedy johnk@opel.COM Second Source, Inc. Annapolis, MD